var select = document.querySelector('select')

var html = document.querySelector('html');

document.body.style.padding = '10px';

function update(bgColor,textColor) {
    html.style.backgroundColor = bgColor;
    html.style.color = textColor
}

select.onchange = function() {
    (select.value === 'tomato') ? update('tomato','skyblue'):update('skyblue','tomato')
}